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previous: Dvaid S. The only way I can think of is to f... -- 1/26/1998 9:34 PM View Thread

Re: Preamp Gain Measurement

1/27/1998 7:11 AM
Steve A.
Re: Preamp Gain Measurement
David and Stephen:  
    I used to use a Casio CZ-101 synth as a make-shift signal generator when I was trying to adjust the bias for my cassette mixdown deck. I'd select a clear patch like "flute" and hold down the key that corresponded to 1000hz by looping the audio cable around synth and would set the level to 1.0 volts or whatever.  
    There are charts in Dan Torres amp books that show the gain for different combinations of anode and cathode resistors at 2 different B+ voltages, but the charts don't indicate the effect of a cathode bypass cap which will increase the gain. In fine-tuning a gain stage by ear, I will try substituting different values for the anode resistors: a higher ohm value will increase the gain, a lower ohm value will lower the gain. If possible, go up and down from the stock value (100k, 150k, 220k, whatever) by 10k at a time. I put together a set of 1/2 watt 2% resistors with all of the values I could find between 100k and 220k for just this purpose.  
    As for cathode bypass caps, switching them in and out of the circuit will make for a decent "gain boost" switch, but you can also experiment with connecting them in series through a 470 to 10k resistor to ground to limit the gain a bit. The advantage with this trick is that you don't lose all of the tonality of the cathode bypass cap.  
Steve Ahola

David S. Thanks for the tips Steve!... -- 1/27/1998 12:34 AM